An integrated gasification combined cycle (hereinafter abbreviated to IGCC) is an electric power generation system in which a fossil fuel such as coal, heavy oil, petroleum residue oil, petroleum coke, and orimulsion is gasified by using a partial oxidation process to produce a synthetic gas mainly containing CO and H2 which is used as a raw material in combined cycle power generation equipment to generate electric power. Exemplary systems include a coal-utilized high-efficiency power generation plant in which an air-blast two-stage entrained bed gasification furnace, wet gas cleaning equipment, and a gas turbine are combined. The IGCC is a system in which the economical efficiency and reliability are improved significantly by achieving simplification and rationalization as power generation equipment. In the IGCC, the efficiency is increased by 10 to 20% as compared with the conventional electric power generation system. In addition, the CO2 emission in the IGCC can be reduced by the same percentage. Further, in the IGCC, handling of ash is easy, because the ash is converted into slag, thus reducing the volume of ash, and it has non-elution property.
In general, flue gas from an existing thermal electric power plant contains mercury derived from coal. Such mercury cannot be removed completely by an ordinary flue gas treatment system (e.g., electrical dust precipitator, wet flue gas desulfurizer, and etc.). Accordingly, some mercury is emitted unless some measures are taken. Mercury is present in gas in a minute amount, and has a very high vapor pressure. In particular, metallic mercury has a property of being insoluble in water. Therefore, it is difficult to completely remove mercury even by recovering it with a dust precipitator or by washing it with a scrubber.
In gas cleaning or refining in the IGCC, for example, approximately 70% of Hg in coal gas can be removed by a water washing process. However, when an absorbing solution used in the water washing process is decompressed from a high pressure to the normal pressure, Hg may be flashed out of the solution and be discharged into an offgas (for example, refer to Japanese Patent Application Publication No. 2003-138277).
In order to remove the mercury discharged into the offgas, a method for adsorbing mercury into activated charcoal to remove it from the offgas has been proposed. FIG. 3 shows a schematic configuration of mercury removal equipment using activated charcoal.
In this equipment, waste water containing mercury sent from a cooling tower is decompressed in a flash drum 10 and is separated into gas and liquid. At this time, most of mercury is separated in a form of being contained in the gas component. This gas component is burned in an offgas furnace 20, and thereafter is treated while flowing down in the order of a dust precipitator (QC/EP) 21 and a flue gas desulfurizer (FGD) 22. The flue gas subjected to flue gas desulfurization passes through an activated charcoal 25 before being discharged, by which harmful components including mercury contained in the flue gas are adsorbed and removed.
The liquid component separated in the flash drum 10 contains an oil content such as tar in the refining of product gas yielded by using, for example, coal etc. as a raw material. Therefore, oil-liquid separation treatment (HC treatment) is performed by using kerosene etc., and the oil content is sent to the offgas furnace 20 as some of fuel. The separated waste water content is subjected to ammonia (NH3) stripping treatment 12 to remove an ammonia content, further being subjected to waste water treatment for removing harmful components as sludge, and is discharged after the waste water treatment.
However, in the conventional method using activated charcoal, activated charcoal must be provided in all lines of generated offgas, so that this method has a problem in that the number of provided activated charcoals increases though the quantity of treated gas is small. Also, the conventional method has many drawbacks in term of maintenance because a location that is unsuitable for the provision of activated charcoal and a location in which activated charcoal cannot be exchanged during operation are included.
Patent Document 1: Japanese Patent Application Publication No. 2003-138277